Sheeted abrasive



Jan. 5,1943. D. Q GUTH j 2,307,461

1SHEEETED ABRASIVE Original Filed llay 2 1928 Patented Jan. 5, 1943 Search Room SHEETED ABRASIVE Durward Ogden Guth, St. Paul, Minn., assignor, by mesne assignments, to Minnesota Mining 85 Manufacturing Company, a corporation of Delaware Application May 2, 1928, Serial No. 274,447 Renewed April 19, 1939 24 Claims.

My present invention relates in general to a treatment of material, preferably in sheet form, and more particularly to the treatment of material for the purpose of obtaining or forming composite structures of which forms of abrasives such as what is commonly known as sandpaper is an example.

Although I hereinafter disclose the practice of my invention in connection with abrasives such as sandpaper, it will be understood that my invention or certain features thereof has a wider field of utility.

Abrasive products as produced at present with varnish materials tend to become brittle, are not, during abrasive action, resistant to all such liquids as are used in sanding operations, such as petroleum; are subject to encounter fire hazards due to operations involved in their manufacture, as will be more fully appreciated by those skilled in the art.

The principal objects of my invention, as will become apparent to those skilled in the art upon due consideration of the disclosure herein, are to overcome some of the objections noted and to produce, by the novel procedure and mode of operation described and set forth herein, an abrasive article of high order of flexibility, strength, extensibility, limpness, resistance to deterioration, abrasive resistance, resistance to slippage and other desirable properties of 5 strength, porosity, absorbency, penetration, waterproofness and abrasive resistance, as obtained by treating the backing materials as more particularly described herein, including the application of surface coating of waterproofing and water insolubilizing ingredients, more particularly hereinafter described, both as to the materials enumerated and the mode of operation described.

In the employment of my present invention for the production of sandpaper or the like, suitable for employment in liquid abrading operations, whether aqueous or organic liquids, I may use as the base a sheeted material, which may be paper, as will conveniently serve the employment contemplated and has as the abrasive such comminuted material (which may be crushed garnet) similarly adapted to serve the function in view. It is preferred that the paper be of the absorbent character and for such purposes crinkled and unsized paper may be used.

The treatment of the base, according to my present invention, involves primarily the association of a protein with the sheeted base of which the paper previously mentioned is the preferred form. The protein is introduced in an aqueous vehicle, leaving a residue in the sheeted base in the nature of a thorough treatment, preferably, however, as a result of saturating the base with the aqueous vehicle containing the protein. The property of the base and the protein residue deposited thereon may be varied as to its flexibility, strength, resistance to deterioration, porosity, absorbency, penetration, elongation, waterproofness and abrasive resistance by including therewith a protein modifying agent. The protein solution with its modifying agents may be varied to leave a residuum serving as a base or backing modifier or a binder for the abrasive particles serving to form the abrasive article. Thus, the proportion of protein and modifying agents in respect to the vehicle therefor may be varied in accordance with the purpose for which the protein is to be used, i. e., a base modifying agent or an adhesive or binder. Thus, also, I may vary the concentration of the protein in its vehicle for purposes of either coating or saturation, taking into account the nature of the residuum and also the degree of penetration and porosity of the sheeted base.

Of the proteins that I may use, I may mention glue, casein and albumen as examples. These proteins may be embodied in vehicles, preferably aqueous, according to methods well-known by those skilled in the art. Proteins of the character mentioned may have added thereto modifying agents which modify the protein itself or materials which extend the protein. The modifying agents may be hygroscopic materials, such as calcium chloride, but it is preferred to use the organic hygroscopic materials, such as glycerine, ethylene glycol, diethylene glycol. Modifying agents which serve as extending agents are rubber, oils, pigments, sulphonated castor oil and the like. Thus, a protein in a vehicle therefor, such as water, may be used to coat, saturate or otherwise impregnate a sheeted material such as paper to leave a residuum, in accordance with properties desired to be imparted to sheeted fabric. The protein residuuim upon the base may be insolubilized or waterproofed by affecting the protein itself or protecting the surface thereof against penetration by the liquid used in sanding operations, in which case the insolubilizing or waterproofing is made resistant to aqueous liquids or organic liquids.

The association of the protein with the base, whether paper or a woven fabric, may be made at the time previous or subsequent to the coating of the sheet with the abrasive particles. This protein residuum may even be introduced, in the case of paper, at the time the base is formed. The protein residuum may extend uniformly throughout the base or may be applied to obtain a satisfactory base by surface treatment and limited penetration.

In its simplest form I may use the protein treatment for the base without modifying agents. An example of such protein solution without modifying agents is as follows:

Example N0. 1

Grams Glue Water 200 The glue and water in proportions above cited are utilized to form a saturating solution for the sandpaper base. The sandpaper base saturated with this solution may have its property of flexibility and strength, controlled by the degree in which the vehicle is removed from the paper, leaving a residuum of protein in various aqueous concentrations, preserved against losses in evaporation preferably by the addition of the modifying agents of the hygroscopic character above mentioned.

It is, however, desirable that the protein as it exists in the fabric base, such as paper, should be resistant to the action of water and for this purpose the protein is preferably directly insolubilized or protected against any solvent action of liquids used in sanding operations by treatments which will be hereinafter described.

A fabric base which serves to protect the fabrics against disintegration by liquids normally used in sanding operations is as follows:

Example No. 2

Grams Casein 100 Calcium hydroxide .4 Sodium hydroxide .4

Ten grams of this mixture is combined with two hundred grams of water to form a solution suitable for saturating the base or backing for sandpaper. The quantity of the protein may be varied in respect to the water content, depending upon the porosity of the paper and the quantity of residuum desired to be left upon the sandpaper base. After drying, the protein is virtually insoluble.

I may impregnate the base or backing material with a solution of a protein and subsequently waterproof or tan the protein by the aid of certain insolubilizing agents. The product such as made as a result of saturation with Example No. 1 or No. 2 may, therefore, be submitted to treatment with certain insolubilizing agents as aldehydes, chrome alum, ferric chloride, tannic acid which serve as waterproofing or tanning agents. As an example, I may treat the sheet, partially or completely dried, after impregnation with the solution of Examples No. l or 2, with a solution of aldehyde consisting of about one part commercial aldehyde and nine parts water by volume.

The product as above made may be rendered more flexible by including with the protein while in solution before impregnation or after impregnation in the paper or fabric base, a flexibility augmenting agent such as glycerine, ethylene glycol, diethylene glycol, sulphonated castor oil or B. T. oil (China-wood oil treated with sulphur to be rendered non-drying) castor oil, cottonseed oil and the like.

Where the flexibility augmenting agent is incorporated directly with the protein solution, a mixture may be made as follows:

Example NO. 3

. Grams Glue 10 Water 200 B. T. oil (sulphur-treated China-wood oil)" 10 The base is impregnated with the above solution and the web or sheet of material treated with formaldehyde as previously described to render the glue insoluble. It will be observed that though I mention glue as a form of protein, for said purposes I may substitute or include partial quantities or casein or albumen. Similarly, I may use the insolubilizing or tanning agents previously described instead of the formaldehyde. Where the base as may be formed with the impregnating solutions previously described is used directly as the support for abrasive particles forming the sandpaper, it is preferred to include in the impregnating solution quantities of a soluble silicate and/or silica gel. These may be added in amounts up to 15 grams and have been found to give additional properties of resistance to abrasion, greater flexibility and resistance to slippage when used for sanding.

Though I previously described the insolubilizing or tanning operation by first impregnating the base and then treating with a solution of a waterproofing or tanning agent, I may incorporate a protein waterproofing or tanning agent directly into the protein solution. The agents best suitable for incorporation with the solution of the protein are the addition compounds between aldehydes and ammonia; aldehydes and sodium bisulfite; aldehydes and hydrogen cyanide, of which hexamethylenetetramine is a well known example; polymers of an aldehyde, such as paraformaldehyde; compounds capable of liberating an aldehyde, such as methyleneparatoludine; carriers including adsorbed aldehydes such as silica gel or charcoal carrying formaldehyde adsorbed thereon. These insolubilizing agents are best used because of their delayed insolubilizing or tanning effect. The aldehydes of the compounds and ingredients above mentioned may be liberated by the action of heat or other physical or chemical means. Decomposition or liberation of the aldehydes may be effected by dry heat. It is preferred, however, for purposes of obtaining a more waterproof and stronger product that the insolubilizing or liberation of the aldehyde be carried out in the presence of moisture.

In insolubilizing the protein, using glue as the example and hexamethylenetetramine as the insolubilizing agent, I have found it desirable to have the ratio of glue to hexamethylenetetramine in the proportion of grams of the former to 4 to 8 grams of the latter. These proportions may be varied below the ratio given, with a diminishing insolubilizing action of the glue. A variation over the higher range of hexamethylenetetramine is not necessary. For certain purposes I prefer to include the insolubilizing agent in the protein and later generate the aldehyde to render the protein inactive. This I may accomplish by the simultaneous action of heat and moisture, that is, heat in the presence of moisture. This treatment may be applied to a base impregnated with the protein solution or to a residuum of the protein in quantities suflicient to form a coating, an adhesive bond for the abrasive particles or a sizing coat, in a manner which will be more particularly described as this description proceeds and likewise, this method of treating the protein has a larger field of utility.

A solution suitable for the treatment as above described is as follows:

Exam ple No. 4

Grams Glue 15 Water 250 Hexamethylenetetramine 1 This solution is used to saturate the fabric which is to form the base. For this purpose it is preferred to use a bibulous, unsized paper. This solution is applied to the base fabric, preferably to saturate the same, dried and then submitted to live steam at a pressure of about 50 pounds. The resulting paper is very strons and flexible, particularly while wet.

The insolubilizing agent need not be generated from the protein solution, in which event the insolubilizing agent may be generated at the same time that the moist heat is applied. For this purpose. the protein, such as glue, may be subjected to the simultaneous action of the insolubilizing agent and moist heat wherein the moist heat is steam and the insolubilizing agent is formaldehyde in a vaporous condition.

I have discovered that when the protein is insolubilized in the presence of moisture. and heat. the resulting product is considerably stronger than if it were not insolubilized in the presence of these.

An example of this treatment is as follows:

Example No. 5

Grams Glue 15 Water 250 The fabric which forms the base, such as paper. is saturated with the above solution and dried. The sheet of material so prepared is subjected to formaldehyde fumes and live steam at 50 pounds pressure simultaneously. In the above example it will be observed that the proportion of glue to water may be modified. depending upon whether it is desired to increase the quantity of residuum and also modify this solution in accordance wi h the absorbent properties of the base fabric which is treated. For mere saturation of the fabric and forming a highly flexible and thin coating, the proportion of glue may be diminished. For purposes of having the residuum act as a binder for abrasive particles or for increasing the thickness of the coating, the glue content may be increased.

Although it is. possible to obtain a desirable condition of the residuum, whether upon the base or in the form previously described, with only a protein solution and the insolubilizing agent activated or liberated at the time of or by the action of heat in the presence of moisture, as above outlined, it is desirable to include certain agents which modify the properties of the protein residuum or the sheet including the prote n residuum Such materials may take the form of hygroscopic materials such as calcium chloride, glycerol. ethylene glycol diethylene glycol and the like or may take the form of materials that dilute or extend the resulting insolubilized protein residuum. These diluting or extending agents which I prefer are organic materials, such as an oil, of which castor oil, cottonseed oil and wood oil will serve as examples. Sulphonated oils, such as sulpho- Search Room nated castor oil may also be used. The inclusion of the organic diluting or extending agents, particularly the oils, has certain additional valuable characteristics. as will appear more fully as this description proceeds. I may also include such a material as a soluble silicate of which an alkali silicate, such as sodium silicate, is preferred. Additionally or alternatively, I may include silica gel. In order to incorporate sodium silicate, I have found it desirable to either increase or suppress the pH value of the protein solutionj"that is, making the pH value of the solution greater or less than pH 7. The following is, therefore, an example of my most preferred method and composition for obtaining a flexible residuum or a flexible base including a protein residuum preferably upon which to bond abrasive particles or for purposes as will appear more fully as this description proceeds. The example is as follows:

Example N0. 6

Grams Glue 15 Water 250 Sodium silicate 10 Hexamethylenetetramine 1 Glycerol 4 Emulsified B. T. oil (sulphur-treated Chinawood oil) 8 The base fabric, such as paper, is treated with this solution preferably by thoroughly saturating the same and afterwards drying. Where a mere coating is desired, the solution is spread to the desired thickness and similarly dried. Where the paper is impregnated, this sheet so treated is dried and treated under pressure as in an autoclave or similar apparatus and subjected to live steam at 50 pounds pressure for about five minutes.

Though I have described as the preferred form, the introduction of all the above ingredients with the protein in the paper base at one operation, I may introduce the modifying agent into the base even after the glue has been insolubilized. The above proportions and their method of application involve the protein residuum wherever th s material may be desired. For purposes of consideration in its preferred application, I make reference to the accompanying drawing forming a part hereof, dealing with an abrasive article in sheet form, such as sandpaper, in which Figure 1 is a section taken of a sheet of fabric such as paper;

Figure 2 is a section similar to Figure 1 with the abrasive layer or grit applied thereto by one form of my invention;

Figure 3 is a section through a base fabric of a modification;

Figure 4 is a section through an abrasive article such as sandpaper in combination with the base shown in Figure 3 but with an abrasive layer or grit applied thereto;

Figure 5 is a section through an abrasive, such as sandpaper, showing another modification;

Figure 6 is a section through an abrasive article showing a still further modification;

Figure 7 is a section through an abrasive article showing a still further embodiment of my invention.

Makin reference to the drawing, the compositions previously described and their method of application may be applied to a sheet of fabric, such as paper, shown in Figure 1, wherein i is a base fabric, such as paper, which has applied thereto a protein, preferably by saturation or impregnation. The application of the protein may be by any of the compositions and methods previously described. Where the impregnating solution containing the protein leaves a relatively high quantity of residuum, this may be directly utilized to adhesively bond to the base I the abrasive particles by the residuum 4 at the superfices. This process is particularly suitable for the production of an abrasive article where the particles of the abrasive are of extremely fine texture.

In the form shown in Figure 2, the base I and the adhesive layer 4, including a protein bond, preferably have a residuum thereof insolubilized by any one of the methods previously described. It will be observed, however, that I may preliminarily form a fabric sheet such as paper treated as above described and apply an auxiliary binder layer 4 for the abrasive particles 5, which may be an additional application of a protein solution subsequently insolubilized, or a binder layer of varnish or varnish-like materials of the resinous or cellulosic type, such as pyroxylin and the like. The base saturated with a protein solution including extending agents of the organic type, such as rubber and the oils or oil material previously mentioned, are particularly suitable for use with an organic binder layer 4 when this organic binder layer is made of varnish of the resin base type or cellulosic base type.

Where it is desired to make a protein treated sheet I more highly resistant to the penetration of liquids used in sanding operations, I may apply to the sheet I additional coatings 2 and 3. These coatings 2 and 3 may be the insolubilized protein, an organic waterproofing coating or a varnish coating of the character above mentioned. Where these coatings are applied, the insolubilizing step after saturating of the base fabric may be omitted, though the omission of this insolubilizing step is not preferred. Where the insolubilizing step is omitted, a higher quantity of water is permitted in the residuum and the layers 2 and 3 will serve to retain this moisture content against undue drying, retaining the base extremely flexible. It will be observed, also, that whether these coats 2 and 3 be for purposes of sealing the base I or as described in connection with Figure 2, for applying an additional adhesive layer 4, the base so treated is further admirably suitable for the varnish materials of the resin or cellulosic type which require maturing by the application of heat, in which event the fabric base such as paper will not lose any of its flexibility or pliabil ity as a result of the heat treatment necessary for maturing the adhesive bond thereon.

In Figure 4 the fabric having the layers 2 and 3 thereon may have additionally applied thereto an adhesive binder layer 4 for bonding to the fabric the abrasive particles 5. In this embodiment, also, the binder layer may be the insolubilized protein or the binder layer of resinous or cellulosic base.

In Figure 5 there is shown a still further embodiment of my invention, in which I is a base fabric, preferably impregnated with a protein, and insolubilized by any of the compositions and methods previously described and 4 is an adhesive binder layer for the abrasive particles 5. This binder layer 4 in this embodiment may be a resinous or cellulosic adhesive bond or a protein bond. The insolubilizing treatment may be omitted in this form and if so omitted I may apply an auxiliary waterproofing size in the form of the layer 6. This layer may be a material of the resinous or cellulosic type and is particularly suitable to prevent the liquid used in sanding operations from penetrating into the interior of the sheet and particularly the binder layer 4 where this layer is the unmodified protein residuum. The binder layer 4 may, however, be the insolubilized protein, in which event the auxiliary waterproofing layer 6 will further augment the waterproofing action.

In the embodiment shown in Figure 6, I is the fabric base saturated with a protein. This fabric base preferably has the protein residuum thereof insolubilized. A binder layer 4 is applied thereto and serves to attach thereon the abrasive particles 5. This binder layer 4 may be a protein residuum, preferably insolubilized. Upon this layer 4 there is applied the auxiliary waterproofing size 6, of the character similar to that previously described in the description of Figure 5. Where the base I includes the untreated protein or the insolubilized protein, I prefer to apply to the lower face of the abrasive article in this embodiment a compensatory and waterproofing layer 2. The layer} may be of the resinous or cellulosic type, in which event the protein in the base I and the binder layer 4 may be untreated. The layers 3 and 6 are preferably of the same character, that is, either of the resinous or cellulosic type or the insolubilized protein type. When of this similar character, they will compensate each other in the variations in atmospheric conditions or those occurring in the treatment so that the abrasive article made will be free from undue curling or warping due to differential drying.

In the embodiment shown in Figure 7, the article is made in all respects similar to the embodiment shown and described in connection with Figure 4, but also including an auxiliary coating 6 of the character as shown and described in connection with the embodiments in Figures 5 and 6. The backing I may be that previously referred to in connection with the embodiments illustrated and described in connection with Figures 1 to 6, and preferably prepared in accordance with the treatments referred to in connection with those embodiments. The coatings 2 and 3 may also be the same as that previously referred to in connection with such views and articles.

The article above made and the methods outlined especially enable the production not only of a flexible sandpaper but also a limp sandpaper. The paper base itself, where such material is used as the fabric base, has unusual strength and is very flexible, especially while wet. This material will also resist deterioration by the liquids used in sanding operations, whether organic or aqueous. Where a sized paper is used, the protein treatment will render the fabric resistant to deterioration by the oils which may be used in the binder layer for the abrasive. The fabric base is particularly resistant to deterioration resulting from heat, particularly that necessary to mature the binder layer. This base material has particular utility with the adhesive binder disclosed in the patent to Okie, No. 1,565,027, December 8, 1925. The fabric base enables the binder to very firmly hold the abrasive particles to the base and enables the bond to be more thoroughly cured without any undue fire hazard, where the bond includes drying oils or volatile solvents. The abrasive article is not slippery to the hand when wet and has therefore a high resistance to slippage when used for sanding and the protein serves to additionally bind the fibres where paper is used to give an unusually strong fabric, even when wet.

The treatment above described further permits of the use of paper of the crinkled or toweled type, which may thus be used to displace abrasive articles having woven cloth backing because of the unusual strength of the paper impar-ted thereto by the composition and the method by which this composition is applied.

Having thus described my invention and illustrated its use, what I claim as new and desire to secure by Letters Patent is:

1. A new article of manufacture in the nature of sandpaper comprising a flexible sheet of fabric, a grit or layer of abrasive particles and an adhesive bond including a protein, glycerine and oil as an extending agent and an aldehyde as an insolubilizing agent, the bond being interposed between said grit and said sheet serving to bind them together.

2. A new article of manufacture in the nature of sandpaper comprising a flexible sheet of fabric, a grit or layer of abrasive particles and an adhesive bond including a protein, a hygroscopic extending agent, a flexibility augmenting agent and a soluble silicate interposed between said grit and said sheet and serving to bind them together.

3. As an article of manufacture a flexible abrasive sheet of fabric, a layer of grit or abrasive particles, a flexible barrier coating interposed between the said grit and said sheet, said barrier coating entering into the fabric, contacting with 'and being anchored to the outer surfaces of some of the fibres of the fabric, an adhesive material interposed between said barrier coating and said grit, said adhesive bonding material and said barrier being immiscible.

4. As an article of manufacture, a flexible abrasive sheet material consisting of a backing sheet of flexible material coated on one side with a non-waterproof material, an adhesive bonding coating in which grit grains are embedded, said non-waterproof material being interposed between the first said material and the adhesive material, said non-waterproof material preventing impregnation of the backing by the adhesive bonding coating holding the abrasive grit.

5. Sandpaper including a paper backing sheet, characterized by a treatment of a porous paper with an agent to impart wet strength thereto, to secure substantially higher wet strength than a sheet not so treated, said backing containing at least one agent adapted to soften the backing and which softening agent retains water in the wet strength imparting agent, said last mentioned agent being Water dispersible and said softened backing having superimposed upon one face thereof a binder for abrasive grits, abrasive grits held by said binder and a water insoluble film forming material intermediate said binder and said sheet.

6. An abrasive article comprising abrasive grains bonded by a protein in preponderating proportions, fiexibilized and insolubilized in situ by an aldehyde liberated from a latent aldehyde generating compound.

'7. An abrasive article comprising abrasive grains bonded by a protein in preponderating proportions and a flexibility augmenting and extending agent of the group consisting of glycerine, ethylene glycol, diethylene glycol, rubber, castor oil, cotton seed oil, sulphonated castor oil, and an insolubilizing agent for the protein, said insolubilizing agent being the decomposition product of a latent aldehyde generating compound the Search Room composition containing the reaction product of the aldehyde generated from said compound in situ.

8. An abrasive article comprising abrasive grains bonded by a protein in preponderating proportions and a flexibility augmenting and extending agent of the group consisting of glycerine, ethylene glycol, diethylene glycol, rubber, castor oil, cotton seed oil, sulphonated castor oil, and an insolubilizing agent for the protein, said insolubilizing agent being the decomposition product of a compound containing an active methylene group the composition containing the reaction product of the aldehyde generated from said compound in situ.

9. Waterproof sandpaper including a sheeted base or backing having flexibility, strength and resistance to deterioriation, comprising highly porous paper and the residuum resulting after treatment with an aqueous dilute solution of a protein, a flexibility augmenting agent, an extending agent and a soluble silicate, a binder coating applied to one side of said backing and abrasive grains held to said backing by said binder.

10. Waterproof sandpaper including a sheeted base or backing having flexibility, strength and resistance to deterioration, comprising highly porous paper and the residuum resulting after treatment with an aqueous dilute solution of a protein, a flexibility augmenting agent, an extending agent, an insolubilizing agent for the protein, a binder coating applied to one side of said backing and abrasive grains held to said backing by said binder.

11. Waterproof sandpaper, including a paper sheet adapted to resist oil penetration, and containing an agent to impart wet strength to the sheet, said agent being a water-dispersible material insolubilized in situ but in its insolubilized form being readily wetted by water and softened by water, and whereby the sheet softened by water has a substantially higher wet strength than a sheet not treated with said agent, a waterresistant sizing superimposed upon the sheet and the wet strengthening agent, a waterproof binder coating comprising synthetic resin applied to at least one side of the sheet, said binder coating being substantially a discrete layer, and abrasive grains held to said sheet by said binder.

12. Waterproof sandpaper, including a paper sheet containing an agent to impart wet strength to the sheet, said agent being a water-dispersible material insolubilized in situ, but in its insolubilized form being readily wetted by water and softened by water, and whereby the sheet softened by water has a substantially higher wet strength than a sheet not treated with said agent, a binder coating comprising synthetic resin applied to the coat side of the sheet, said binder coating being substantially a discrete layer, and abrasive grains held to said sheet by said binder.

13. Waterproof sandpaper, including a paper sheet containing an agent to impart wet strength to the sheet, said agent being a water-dispersible material insolubilized in situ but in its insolubilized form being readily wetted by water and softened by water, and whereby the sheet softened by water has a substantially higher wet strength than a sheet not treated with said agent, a water-resistant treatment applied to the back side of the sheet superimposed upon the sheet and the wet strengthening agent, a binder coating comprising synthetic resin applied to the coat side of the sheet said binder coating being substantially a discrete layer, and abrasive grains held to said sheet by said binder.

14. Waterproof sandpaper, including a paper backing containing tanned glue as an agent to impart wet strength said tanned glue being insolubilized in situ but in its insolubilized form being readily wetted by water and softened by water and whereby the backing softened by water has a substantially higher wet strength than a backing not treated with said agent, a water-resistant paper treatment superimposed upon the backing and the wet strengthening agent, a binder for abrasive grains consisting of synthetic resin and constituting substantially a discrete layer, and abrasive grains held to said backing by said binder.

15. The process of producing coating abrasives comprising using paper of suitable porosity, treating the paper with an agent to impart wet strength to the sheet including an agent which retains water in the wet strength imparting agent, applying a water resistant treatment to the sheet and then applying a waterproof bond selected from the group consisting of varnishes and resins and abrasive particles to the sheet so treated and maturing the bond upon the sheet.

16. Waterproof sandpaper including a porous base paper containing an agent to impart wet strength to the sheet, said agent being a water dispersible material insolubilized in situ but in its insolubilized form being readily wetted and softened by water and whereby the sheet wetted with water has a higher wet strength than a sheet not treated by said agent, and a binder coating of a waterproofing material applied to the sheet selected from the group consisting of varnishes and resins, said binder coating being substantially a discrete layer of abrasive grains held to said sheet by said binder.

17. Sandpaper provided with a surface layer of abrasive particles and comprising a highly absorptive paper base containing only insolubilized, glycerinated glue as its strengthening agent and carrying a bond-coating of set or dried drying oil and resin by which said particles are bonded to said base, said glue being present in said base in amount to increase vastly the wet strength of said base but said base, despite its content of said glue, being readily penetrated and softened by water without significant effect on the bonding effectiveness of said bond-coating on said particles, whereby said sandpaper may be soaked and flexibilized in water and rumpled preparatory to its use without danger of tearing said base or causing said particles to shed therefrom.

18. Sandpaper provided with a surface layer of abrasive particles and comprising a base paper backing containing insolubilized glycerinated glue as a strengthening agent and having a water insoluble oil superimposed upon and penetrating substantially uniformly throughout the area of said base paper containing said insolubilized glycerinated glue, said treated paper carrying a waterproof binder coating comprising synthetic resin by which said abrasive particles are bonded to said base, said insolubilized glue being present in said base in an amount effective to increase vastly the wet strength of said base, said base containing said insolubilized glue being softened by saidglycerine when dry but despite its content of said insolubilized glue and despite the presence of water insoluble oil being readily penetrated and further softened by water without significant effect on the bonding effectiveness of said bond coating on said particles, whereby said sandpaper may be soaked and fiexibilized in water and does not tear or shed its abrasive particles in normal handling, bending, and use.

19. Waterproof sandpaper, including a paper backing having substantially uniformly distributed therethrough at least one agent to soften the backing, said agent being a. water soluble polyhydric alcohol selected from the group consisting of glycerine, ethylene glycol, and diethylene glycol, said softened backing having superimposed upon and being substantially uniformly penetrated throughout its area with a semi-drying oil, a waterproof binder for abrasive grains, and abrasive grains held to said backing by said binder.

20. Waterproof sandpaper, including a paper backing sheet containing at least one agent to impart wet strength to the backing, said agent being a water-dispersible material insolubilized in situ, but in its insolubilized form being readily wetted by water and softened by water, and whereby the sheet softened by Water has a substantally higher wet strength than a sheet not treated with said agent, said backing containing at least one agent adapted to soften the backing, said last mentioned agent being a water soluble polyhydric alcohol selected from the group consisting of glycerine, ethylene glycol and diethylene glycol and said softened backing having superimposed upon and being substantially uniformly penetrated throughout its area with a semi-drying oil, a waterproof binder for abrasive grits, and abrasive grits held to said sheet by said binder.

21. Waterproof sandpaper, including a. paper backing sheet containing a wet strength treatment of tanned glue, said glue being tanned or insolubilized in situ, but in its insolubilized form being readily wetted by water and softened by water and whereby the sheet softened by water has a substantially higher wet strength than a sheet not treated with said tanned glue, and a water soluble polyhydric alcohol softener for both said paper and said tanned glue selected from the group consisting of glycerine, ethylene glycol and diethylene glycol, and said softened backing having superimposed upon and being substantially uniformly penetrated throughout its area with a semi-drying oil, a binder for abrasive grains, and abrasive grains held to said backing by said binder.

22. Waterproof sandpaper including a paper backing sheet containing at least one agent to impart wet strength to the backing, said agent being a water dispersible material insolubilized in situ but in its insolubilized form being readily wetted by water and softened by water, and whereby the sheet softened by water has a sub stantally higher wet strength than a sheet not treated with said agent, said backing containing at least one agent adapted to soften the backing, said last mentioned agent being water dispersible and less volatile than known softening agents for glue including the glycols and glycerine, and said softened backing having superimposed upon and being substantially uniformly penetrated throughout its area with a semi-drying oil, a waterproof binder for abrasive grits, and abrasive grits held to said sheet by said binder.

23. Sandpaper including a paper backing sheet containing at least one agent to impart wet strength to the backing, said agent being a water dispersible material insolubilized in situ but in its insolubilized form being readily wetted by water and softened by water, and whereby the sheet softened by water has a. substantially higher wet strength than a sheet not including said agent, said backing containing at least one agent adapt-' ed to soften the backing, said last mentioned agent being water dispersible and said softened backing having superimposed upon one face thereof, a binder for abrasive grits, abrasive grits held by said binder, and a water insoluble film 1 Search Room forming material intermediate said binder and sheet.

24. Abrasive paper comprising abrasive grains, a binder for the abrasive grains, and a paper backing permeated with the residuum of a dilute solution of protein, water, ammonia, a soluble silicate, an aldehyde, a hygroscopic agent for fiexibilizing the protein and an oil.

DURWARD OGDEN GUTH.

"I l; f

D CERTIFICATE OF CORRECTION.

i atent No. 250711.61. January 5, 1%.}.

DURWARD OGDEN GUTH.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, first column, line L5, in the table, for Calcium hydroxide .Lp' read -Calcium hydroxide 7.14."; page 5, first column, line 14.6, after "example" insert a comma; page 11., second column, line 25, for layer 2" read --layer 5"; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 11th day of May, A. D. 191;

Henry Van Arsdale, (Seal) Acting Commissioner of Patents. 

